A pacemaker is implantable cardiac stimulation device for implant within a patient that analyzes an IEGM to detect various arrhythmias such as an abnormally slow heart rate (bradycardia) or an abnormally fast heart rate (tachycardia) and delivers electrical pacing pulses to the heart in an effort to remedy the arrhythmias. An implantable cardioverter-defibrillator (ICD) additionally detects atrial fibrillation (AF) or ventricular fibrillation (VF) and delivers electrical shocks to terminate fibrillation.
For many patients, particularly those with congestive heart failure (CHF), it is desirable to identify a set of control parameters for controlling the operation of the pacemaker or ICD that will yield optimal cardiac performance (also referred to as hemodynamic performance). Cardiac performance is a measure of the overall effectiveness of the cardiac system of a patient and is typically represented in terms of stroke volume or cardiac output. Stroke volume is the amount of blood ejected from the left ventricle during systole in a forward direction. Cardiac output is the volume of blood pumped by the left ventricle per minute (or stroke volume times the heart rate). In view of the importance of maintaining optimal cardiac performance, especially for patients with compromised cardiac function, it would be desirable to provide improved techniques for use with pacemakers or ICDs or other implantable cardiac stimulation devices for identifying pacing control parameters that optimize cardiac performance, particularly to reduce the degree of heart failure and valvular regurgitation. It is to this end that aspects of the invention are generally directed.
A useful control parameter for optimizing cardiac performance is the atrioventricular pacing delay, referred to herein is the A-VP delay, which for dual chamber devices specifies the time delay between a paced or sensed atrial event and a paced ventricular event. Sensed events (i.e. intrinsic or native events) are also referred to as depolarization events as these events are representative of electrical depolarization of myocardial tissue. Paced events are also referred to herein as evoked responses. Paced events in the atria are triggered by A-pulses generated by the implantable device. Paced events in the ventricles are triggered by V-pulses also generated by the implantable device. Note that, herein, “A” is generally used to refer to atrial events, whether paced or sensed. “V” is used to generally refer to ventricular events, whether paced or sensed. In circumstances where it is necessary to distinguish between paced and sensed events, an “S” or “P” is appended. Hence, AS refers to a sensed atrial event, whereas AP refers to paced atrial event. VS refers to a sensed ventricular event, whereas VP refers to a paced ventricular event. Thus, A-VP generally represents the delay between either a paced or sensed atrial event and a paced ventricular event. AS-VP specifically refers to the delay between a sensed atrial event and the paced ventricular event; whereas AP-VP specifically refers to the delay between a paced atrial event and the paced ventricular event.
In addition, where appropriate, an “L” or “R” subscript is employed herein to distinguish between the left and right chambers of the heart. For example, APR refers to a paced event in the right atrium. VSR refers to a sensed event in the right ventricle. Hence, APR−VSR represents the delay between a paced event in the right atrium and a sensed event in the right ventricle. Also, where appropriate, a “PEAK” or “END” subscript is employed herein to distinguish between the peak and end of a given event. For example, ASPEAK represents the peak of a sensed atrial event; whereas ASEND represents the end of the sensed atrial event. The term “intrinsic delay”, as used herein, refers to the delay between a paced or sensed event in one chamber and a subsequent sensed depolarization in another chamber. For example, an “intrinsic atrioventricular delay” refers to the delay between a paced or sensed atrial event and a subsequent sensed ventricular event, e.g. an AS-VS or AP-VS delay. Also, a “T” is used herein to identify repolarization events. For example, AT refers to an atrial repolarization; whereas VT refers to a ventricular repolarization. Note that the A, V and T events, whether paced or sensed, are all features of the IEGM signal sensed and recorded by the implantable device. The features are also observable in surface electrocardiogram (EKG) signals obtained via leads temporarily affixed to the chest of the patient. The corresponding feature of an AS event observed within the surface EKG is referred to as a P-wave. The corresponding feature of a VS event observed within the surface EKG is referred to as an R-wave. The corresponding feature of a repolarization event observed within the surface EKG is referred to as a T-wave. Finally, note that the VS event of the IEGM is also often referred to as a QRS complex.
In normal patients, the electrical conduction through the atrioventricular node is intact, and the body automatically adjusts the intrinsic atrioventricular delay (AS-V) via the circulating hormones and the autonomic nervous system according to its physiologic state. It is well known, for example, that in normal patients the intrinsic atrioventricular delay shortens with increasing heart rate associated with a physiologic stress such as exercise. For patients with abnormal atrioventricular node conduction or complete heart block, a pacemaker can control the A-VP delay (i.e. either the AS-VP delay, the AP-VP delay or both) by delivering a ventricular pacing pulse at a software-controlled delay after an atrial pace or atrial sensed event. Since the optimum A-VP delay varies from person to person, this parameter should be optimized on an individual basis.
Conventionally, the physician attempts to program the A-VP delay (or other parameters) for a given patient by using an external programmer to control the device implanted within the patient to cycle through a set of different A-VP delay values. For each value, the implanted device paces the heart of the patient for at least a few minutes to permit hemodynamic equilibration, then the physician records a measure of the resulting cardiac performance, measured, for example, using Doppler echocardiography. The A-VP delay value that yields the best cardiac performance is then selected and programmed into the device. However, this is a time consuming and potentially expensive procedure. As a result, some physicians do not bother to optimize A-VP delay in many of their patients. Rather, A-VP delay is merely set to a default value and is adjusted only if the patient does not respond well to pacing therapy or complains that they do not feel well.
Hence, many patients are not paced at their particular optimal A-VP delay value and thus do not obtain the maximal potential benefit from the improved cardiac performance that could otherwise be gained. Moreover, even in circumstances wherein A-VP delay is optimized by the physician using, for example, Doppler echocardiography, the time and associated costs are significant. In addition, the optimal A-VP delay for a particular patient may change with time due to, for example, progression or regression in CHF, changes in medications, and/or changes in overall fitness. However, with conventional optimization techniques, the A-VP delay is re-optimized, if at all, only during specially scheduled follow-up sessions with the physician to allow access to the noninvasive testing equipment such as Doppler-echocardiography, which sessions may be months or perhaps years apart.
Accordingly, it is would be highly desirable to provide improved techniques for more easily and reliably determining optimal or otherwise preferred A-VP delay values for a particular patient. Preferably, such techniques would be designed so as to be performed by the implantable device itself using only IEGM data, so that Doppler echocardiography or other expensive and time consuming cardiac performance monitoring techniques are no longer required. This permits the optimal A-VP delay to be frequently and automatically updated so as to respond to changes within the patient.
Many of these needs have been met by techniques set forth in U.S. patent application Ser. No. 10/928,586, of Bruhns et al., entitled “System and Method for Determining Optimal Atrioventricular Delay based on Intrinsic Conduction Delays”, filed Aug. 27, 2004, which is incorporated by reference herein. Briefly, techniques are provided therein where both the intrinsic inter-atrial conduction delay and the intrinsic atrioventricular conduction delay are determined for the patient and then preferred A-VP delay values are derived therefrom. In one example, the technique uses only IEGM signals and surface EKG signals and hence can be performed by an external programmer without requiring Doppler echocardiography or other cardiac performance monitoring techniques. In another example, wherein the implanted device is equipped with a coronary sinus lead, the technique uses only IEGM signals and hence can be performed by the device itself.
Although the techniques of Bruhns et al. are effective, it would be desirable to provide alternative techniques for determining optimal or otherwise preferred A-VP delay values for a patient, particularly techniques that do not require the use of a surface EKG, and it is to that end that the present invention is more specifically directed.